Gelable composition

ABSTRACT

A composition including a polymer and a liquid, wherein the polymer exhibits lower solubility in the liquid at room temperature but exhibits greater solubility in the liquid at an elevated temperature, wherein the composition gels when the elevated temperature is lowered to a first lower temperature without agitation, wherein the viscosity of the composition results from a process comprising (a) dissolving at the elevated temperature at least a portion of the polymer in the liquid; (b) lowering the temperature of the composition from the elevated temperature to the first lower temperature; and (c) agitating the composition to disrupt any gelling, wherein the agitating commences at any time prior to, simultaneous with, or subsequent to the lowering the elevated temperature of the composition to the first lower temperature, wherein the amount of the polymer dissolved in the liquid at the elevated temperature ranges from about 0.2% to about 5% based on the total weight of the polymer and the liquid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of co-pending U.S.application Ser. No. 10/720,597 (filing date Nov. 24, 2003), from whichpriority is claimed, the disclosure of which is totally incorporatedherein by reference, which is a divisional application of U.S.application Ser. No. 10/273,896 (filing date Oct. 17, 2002, now issuedas U.S. Pat. No. 6,890,868B2) from which priority is claimed, thedisclosure of which is totally incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with United States Government support underCooperative Agreement No. 70NANBOH3033 awarded by the National Instituteof Standards and Technology (NIST). The United States Government hascertain rights in the invention.

BACKGROUND OF THE INVENTION

Polymer thin film transistors have potential applications forfabricating low-cost integrated circuits for large-area/low-endelectronic devices such as active matrix liquid crystal displays,electronic paper, smart cards, radio frequency identification tags, andthe like. They have the added advantages of being mechanically durableand compatible with flexible substrates, thus offering the potential offabricating structurally flexible electronic devices. Two criticalrequirements for these low-cost applications are sufficient chargecarrier mobility and solution processability. Higher charge carriermobility can be achieved through enabling material design and processinnovation as disclosed in PCT WO 00/79617 A1 and Yiliang Wu et al.,U.S. Ser. No. 10/273,901 (attorney docket number D/A1714; filed Oct. 17,2002) titled “Process and Device Using Self-Organizable Polymer.”Solution processability of materials at room temperature or othertemperatures slightly above room temperature is generally advantageousdue to the lower energy requirement and the simplification in equipment.However, certain polymers may gel at these temperatures which rendersthe gelled composition unable to be satisfactorily solution coated.Thus, there is a need, which the present invention addresses, for newtechniques to enable the fabrication of polymer thin film transistors ata temperature lower than an elevated temperature using polymers that arecapable of gelling.

The following documents also may be relevant:

F. Brustolin et al., “Highly Ordered Structures of AmphiphilicPolythiophenes in Aqueous Media,” Macromolecules, Vol. 35, pp. 1054-1059(published on web Jan. 3, 2002).

G. Dufresne et al., “Thermochromic and Solvatochromic ConjugatedPolymers by Design,” Macromolecules, Vol. 33, pp. 8252-8257 (publishedon web Sep. 30, 2000).

M. Leclerc, “Optical and Electrochemical Transducers Based onFunctionalized Conjugated Polymers, Adv. Mater., Vol. 11, No. 18, pp.1491-1498 (1999).

SUMMARY OF THE DISCLOSURE

The present invention is accomplished in embodiments by providing aprocess comprising:

selecting a composition including a polymer and a liquid, wherein thepolymer exhibits lower solubility in the liquid at room temperature butexhibits greater solubility in the liquid at an elevated temperature,wherein the composition gels when the elevated temperature is lowered toa first lower temperature without agitation;

dissolving at the elevated temperature at least a portion of the polymerin the liquid;

lowering the temperature of the composition from the elevatedtemperature to the first lower temperature;

agitating the composition to disrupt any gelling, wherein the agitatingcommences at any time prior to, simultaneous with, or subsequent to thelowering the elevated temperature of the composition to the first lowertemperature;

depositing a layer of the composition wherein the composition is at asecond lower temperature lower than the elevated temperature; and

drying at least partially the layer.

In embodiments, there is also provided a process comprising:

selecting a composition including a self-organizable polymer and aliquid, wherein the polymer exhibits lower solubility in the liquid atroom temperature but exhibits greater solubility in the liquid at anelevated temperature, wherein the composition gels when the elevatedtemperature is lowered to a first lower temperature without agitation;

dissolving at the elevated temperature at least a portion of the polymerin the liquid;

lowering the temperature of the composition from the elevatedtemperature to the first lower temperature;

agitating the composition to disrupt any gelling, wherein the agitatingcommences at any time prior to, simultaneous with, or subsequent to thelowering the elevated temperature of the composition to the first lowertemperature;

depositing via solution coating a layer of the composition wherein thecomposition is at a second lower temperature lower than the elevatedtemperature; and

drying at least partially the layer.

There is further provided in embodiments a thin film transistorcomprising:

an insulating layer;

a gate electrode;

a structurally ordered semiconductor layer;

a source electrode; and

a drain electrode,

wherein the insulating layer, the gate electrode, the semiconductorlayer, the source electrode, and the drain electrode are in any sequenceas long as the gate electrode and the semiconductor layer both contactthe insulating layer, and the source electrode and the drain electrodeboth contact the semiconductor layer,

wherein the semiconductor layer is prepared by a process comprising:

selecting a composition including a self-organizable polymer and aliquid, wherein the polymer exhibits lower solubility in the liquid atroom temperature but exhibits greater solubility in the liquid at anelevated temperature, wherein the composition gels when the elevatedtemperature is lowered to a first lower temperature without agitation;

dissolving at the elevated temperature at least a portion of the polymerin the liquid;

lowering the temperature of the composition from the elevatedtemperature to the first lower temperature;

agitating the composition to disrupt any gelling, wherein the agitatingcommences at any time prior to, simultaneous with, or subsequent to thelowering the elevated temperature of the composition to the first lowertemperature;

depositing via solution coating a layer of the composition, resulting inthe semiconductor layer, wherein the composition is at a second lowertemperature lower than the elevated temperature; and

drying at least partially the layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects of the present invention will become apparent as thefollowing description proceeds and upon reference to the Figures whichrepresent illustrative embodiments:

FIG. 1 represents a first embodiment of a thin film transistor madeusing the present process;

FIG. 2 represents a second embodiment of a thin film transistor madeusing the present process;

FIG. 3 represents a third embodiment of a thin film transistor madeusing the present process; and

FIG. 4 represents a fourth embodiment of a thin film transistor madeusing the present process.

Unless otherwise noted, the same reference numeral in different Figuresrefers to the same or similar feature.

DETAILED DESCRIPTION

Any polymer which is capable of gelling may be used in the presentinvention. The phrase “capable of gelling” refers to when a compositionincluding the polymer and a liquid is subjected first to an elevatedtemperature (exemplary elevated temperatures are discussed herein) andthen to a first lower temperature (exemplary first lower temperaturesare discussed herein), where gelling occurs when the temperaturereduction is accomplished without agitation. This gelling is referred toas physical gelling as no covalent bonding occurs. In the absence ofagitation, such gelling typically occurs in a timeframe ranging forexample from about 5 seconds to about one hour. The term “gelling” or“gel” refers to formation of a three-dimensional polymer network of apolymer in a liquid through intermolecular interaction such as hydrogenbonding, van der Waals interactions, while the liquid is adsorbed in thethree-dimensional network.

The polymer may be considered to exhibit poor solubility in a liquidwhen the concentration of the polymer in a saturated solution in thatliquid is not high enough to make a thin polymer layer that is usefulfor the intended applications by common deposition techniques.Generally, when the concentration of the polymer in a particular liquidis below about 0.1 percent by weight, its solubility in that liquid isdeemed to be poor. Even though the polymer may exhibit low solubility ina liquid at room temperature, its solubility can generally be increasedby heating above room temperature.

When the concentration is higher than about 0.2 percent by weight, thepolymer is considered to exhibit reasonable solubility as a useful thinpolymer layer may be fabricated from this solution using commondeposition processes.

The phrase “room temperature” refers to a temperature ranging from about22 to about 25 degrees C.

In embodiments, one, two, three or more different polymers may beemployed.

The polymer may be for example a self-organizable polymer. Molecularself-organization refers to the ability of molecules to organizethemselves into a higher molecular structural order in response to astimulus such as a change in solvency of the liquid for the polymer.Self-organizable polymers include for example conjugated polymers suchas for instance polythiophenes. Exemplary polythiophenes include forinstance the following:

where n is from about 5 to about 5,000. Suitable polythiophenes aredisclosed in U.S. Ser. No. 10/042,356 (Attorney Docket No. D/A1334)which issued as U.S. Pat. No. 6,621,099, U.S. Ser. No. 10/042,358(Attorney Docket No. D/A1332) which issued as U.S. Pat. No. 6,770,904,and U.S. Ser. No. 10/042,342 (Attorney Docket No. D/A1333) which hasbeen published as US Published Application 2003/0160234, the disclosuresof which are totally incorporated herein by reference.

In the composition, the polymer or polymers are completely dissolved orpartially dissolved in a liquid at an elevated temperature. Agitationmay be optionally employed to aid the dissolution. Undissolved polymermay be optionally removed by filtration. The amount of the polymerdissolved in the liquid at the elevated temperature may range forexample from about 0.1% to as much as about 50% by weight of thepolymer. In embodiments, the concentration of the polymer in the liquidat the elevated temperature ranges for example from about 0.1% to about30% by weight, particularly from about 0.2% to about 5% by weight, basedon the total weight of the liquid and the polymer.

Heat is employed to aid the dissolution of the polymer at an elevatedtemperature for a period of time ranging for instance from about 1minutes to about 24 hours, particularly from about 10 minutes to about 4hours.

As used herein, the phrase “elevated temperature” refers to atemperature ranging from above room temperature to the boiling point orhigher of the chosen liquid (at one atmosphere or higher pressure), forexample from about 40 to about 180 degrees C., particularly from about50 to about 120 degrees C.

The liquid may be for instance dichloroethane, chloroform,tetrahydrofuran, chlorobenzene, dichlorobenzene, trichlorobenzene,nitrobenzene, toluene, xylene, mesitylene,1,2,3,4-tetrahydronaphthelene, dichloromethane, 1,2-dichloroethanetrichloroethane, 1,1,2,2,-chloroethane, or a mixture thereof.

Although the composition can be used for device preparation at theelevated temperature, the use of the elevated temperature will increasethe manufacturing cost. Thus, to lower the manufacturing cost, thetemperature of the composition is lowered from the elevated temperatureto the first lower temperature. The first lower temperature may be atemperature ranging from below room temperature to below the elevatedtemperature such as for example from about 10 to about 60 degrees C.,particularly from about 20 to about 30 degrees C., and especially atroom temperature. In embodiments, the temperature is lowered from theelevated temperature to the first lower temperature by an amount rangingfor instance from about 10 to about 150 degrees C., particularly fromabout 20 to about 80 degrees C. The composition is maintained at thefirst lower temperature for a time period ranging for example from about10 minutes to about 10 hours, particularly from about 30 minutes toabout 4 hours.

To disrupt any gelling when the elevated temperature is lowered to thefirst lower temperature, the composition is subjected to agitationwherein the agitating commences at any time prior to, simultaneous with,or subsequent to the lowering the elevated temperature of thecomposition to the first lower temperature. The agitation is maintainedfor a sufficient time to disrupt any gelling of the composition such asan agitation time ranging for example from about 5 minutes to about 20hours. The intensity of the agitation may be constant or may varythroughout the agitation time. Exemplary agitation methods include forinstance, stirring and homogenization with the mixing speed ranging forexample from about 1000 rpm to about 5000 rpm, and ultrasonic vibrationwith a sonicator wattage ranging for example from about 100 W to about400 W and a sonicator frequency ranging for example from about 20 kHz toabout 42 kHz.

Gelling is generally undesirable since a composition turned to a gel isdifficult to solution coat at room temperature; but gelling is anindicator of increased structural order of certain self-organizablepolymers. The composition is subjected to agitation as described hereinto disrupt any gelling. In embodiments, visibly observable gelledmaterial may exist despite the agitation; such gelled material survivingthe agitation may be optionally removed by for example filtration.

In embodiments of the present process, the polymer molecules may cometogether to form structurally ordered polymer aggregates in the liquidduring the agitation. The polymer aggregates are for example nanometersized with a size ranging for instance from about 10 nm to about 500 nm,particularly from about 150 nm to about 300 nm.

When a self-organizable polymer is used, the polymer aggregates in theliquid may exhibit in embodiments structural ordering, yieldingstructurally ordered polymer aggregrates. The phrase “structurallyordered polymer aggregates” refers to the aggregation of polymermolecules wherein the spatial orientations or arrangements of themolecules relative to their surrounding neighboring molecules within theaggregation are orderly in nature. For instance the polymer moleculesmay align themselves with their backbones parallel to one another.Changes in molecular ordering of the polymer in a composition may bemonitored by spectroscopic methods, for instance, absorptionspectroscopy, optical spectroscopy, NMR, light scattering and X-raydiffraction analysis, and by transmission electron microscopy. A knownexample is regioregular poly(3-alkylthiophene-2,5-diyl)s which formsπ-stacked lamellar structures as a result of its side chain alignment asdisclosed in the reference, “Extensive Studies on π-Stacking ofPoly(3-alkylthiophene-2,5-diyl)s and Poly(4-alkylthiazole-2,5-diyl)s byOptical Spectroscopy, NMR Analysis, Light Scattering Analysis and X-rayCrystallography” by T. Yamamoto, et al., J. Am. Chem. Soc. (1998), Vol.120, pp. 2047-2058. The existence of the structural order (of thepolymer aggregates) is supported by for example spectroscopy where in anabsorption spectrum the absorption maxima shifts toward longerwavelengths together with the appearance of absorption fine structures(e.g., vibronic splitting). In embodiments, the formation of polymeraggregates was verified by absorption spectroscopy measurement and bydirect observation under transmission electron microscopy.

In embodiments, the composition may be a dispersion including thepolymer aggregates and the liquid, wherein the dispersion may be stablefor a period of time ranging for example from about a few hours to morethan one month. The stability of the dispersion refers to its visualclarity with no visible separation into solid and liquid phases.

In embodiments, a different liquid may be added that is less or notcapable of dissolving the polymer compared to the liquid, i.e., theliquid is a better solvent than the different liquid (the solventproperties of the liquid and different liquid are compared at the sametemperature). It is believed that addition of the different liquid maychange the conformation of the polymer chains and disrupt or change theintermolecular interactions, which minimize the likelihood of gelling.The different liquid is added in an amount ranging from about 1% toabout 80% by volume based on the total volume of the liquid and thedifferent liquid over a period of time ranging for instance from about 1minutes to about 4 hours, particularly from about 10 minutes to about 1hour. The different liquid may be added at any suitable point such asfor example during the dissolution of at least a portion of the polymerin the liquid at the elevated temperature or during the lowering thetemperature of the composition from the elevated temperature to thefirst lower temperature. The temperature of the different liquid duringits addition to the composition may be the same or different from thetemperature of the composition.

The different liquid may be for instance methanol, ethanol, isopropanol,hexane, heptane, acetone, and water. Therefore, the resultantcomposition is comprised of the polymer or polymers and the combinationof the liquid and the different liquid which can be the combination ofchlorobenzene/hexane, chlorobenzene/heptane, chloroform/methanol,tetrahydrofuran/methanol, and tetrahydrofuran/water. Agitation asdescribed herein is used to minimize the formation of gelling of theresultant composition.

Any suitable technique may be used to deposit a layer of thecomposition. In embodiments, solution coating may be used. The phrase“solution coating” refers to any composition compatible coatingtechnique such as spin coating, blade coating, rod coating, screenprinting, stamping, ink jet printing, and the like.

During the depositing the layer of the composition, the composition isat a second lower temperature. The second lower temperature may be atemperature ranging from below room temperature to below the elevatedtemperature such as for example from about 10 to about 40 degrees C.,particularly from about 20 to about 30 degrees C., and especially atroom temperature. The second lower temperature and the first lowertemperature may be the same or different from one another. Where thesecond lower temperature and/or the first lower temperature are belowroom temperature, suitable cooling apparatus may be employed toaccomplish this. In embodiments, both the second lower temperature andthe first lower temperature are at room temperature.

The deposited layer is at least partially dried, especially completelydried, using any suitable technique to remove the liquid (and if usedthe different liquid). When dried, the polymer aggregates collapsetogether and coalesce, resulting in the formation of a continuous film.Where the polymer is a self-organizable polymer, this continuous filmmay contain in embodiments polymer that is structurally ordered and thuscorresponds to a structurally ordered layer. Drying techniques mayinvolve for instance: directing one or more streams of air (at roomtemperature or at an elevated temperature) at the layer; “natural”evaporation from the layer (i.e., evaporation at room temperaturewithout using an air stream), heating the layer while optionallyapplying a vacuum, or a combination of drying techniques. In embodimentswhere heat is employed in the drying technique, the elevated temperaturemay range for instance from about 40 to about 120 degrees C. at normalor reduced pressures, for a period of time ranging for instance fromabout 10 minutes to about 24 hours. The dry thickness of the layer isfor example from about 10 nanometers to about 1 micrometer or forexample from about 10 to about 150 nanometers. In embodiments, theresulting layer is a structurally ordered layer which may be thesemiconductor layer of an electronic device such as a thin filmtransistor.

In embodiments, the present process may be used whenever there is a needto form a semiconductor layer in an electronic device. The phrase“electronic device” refers to micro- and nano-electronic devices suchas, for example, micro- and nano-sized transistors and diodes.Illustrative transistors include for instance thin film transistors,particularly organic field effect transistors. The present process,however, may be used not just in fabricating electronic devices but inany process where it is difficult to deposit a layer including thepolymer because of the tendency of the polymer to form a gel undercertain circumstances.

In FIG. 1, there is schematically illustrated a thin film transistor(“TFT”) configuration 10 comprised of a substrate 16, in contacttherewith a metal contact 18 (gate electrode) and a layer of aninsulating layer 14 on top of which two metal contacts, source electrode20 and drain electrode 22, are deposited. Over and between the metalcontacts 20 and 22 is an organic semiconductor layer 12 as illustratedherein.

FIG. 2 schematically illustrates another TFT configuration 30 comprisedof a substrate 36, a gate electrode 38, a source electrode 40 and adrain electrode 42, insulating layer 34, and an organic semiconductorlayer 32.

FIG. 3 schematically illustrates a further TFT configuration 50comprised of a heavily n-doped silicon wafer 56 which acts as both asubstrate and a gate electrode, a thermally grown silicon oxideinsulating layer 54, and an organic semiconductor layer 52, on top ofwhich are deposited a source electrode 60 and a drain electrode 62.

FIG. 4 schematically illustrates an additional TFT configuration 70comprised of substrate 76, a gate electrode 78, a source electrode 80, adrain electrode 82, an organic semiconductor layer 72, and an insulatinglayer 74.

The composition and formation of the semiconductor layer are describedherein.

The substrate may be composed of for instance silicon, glass plate,plastic film or sheet. For structurally flexible devices, plasticsubstrate, such as for example polyester, polycarbonate, polyimidesheets and the like may be preferred. The thickness of the substrate maybe from amount 10 micrometers to over 10 millimeters with an exemplarythickness being from about 50 to about 100 micrometers, especially for aflexible plastic substrate and from about 1 to about 10 millimeters fora rigid substrate such as glass or silicon.

The compositions of the gate electrode, the source electrode, and thedrain electrode are now discussed. The gate electrode can be a thinmetal film, a conducting polymer film, a conducting film made fromconducting ink or paste or the substrate itself, for example heavilydoped silicon. Examples of gate electrode materials include but are notrestricted to aluminum, gold, chromium, indium tin oxide, conductingpolymers such as polystyrene sulfonate-dopedpoly(3,4-ethylenedioxythiophene) (PSS-PEDOT), conducting ink/pastecomprised of carbon black/graphite or colloidal silver dispersion inpolymer binders, such as Electrodag available from Acheson ColloidsCompany. The gate electrode layer can be prepared by vacuum evaporation,sputtering of metals or conductive metal oxides, coating from conductingpolymer solutions or conducting inks by spin coating, casting orprinting. The thickness of the gate electrode layer ranges for examplefrom about 10 to about 200 nanometers for metal films and in the rangeof about 1 to about 10 micrometers for polymer conductors. The sourceand drain electrode layers can be fabricated from materials whichprovide a low resistance ohmic contact to the semiconductor layer.Typical materials suitable for use as source and drain electrodesinclude those of the gate electrode materials such as gold, nickel,aluminum, platinum, conducting polymers and conducting inks. Typicalthicknesses of source and drain electrodes are about, for example, fromabout 40 nanometers to about 1 micrometer with the more specificthickness being about 100 to about 400 nanometers.

The insulating layer generally can be an inorganic material film or anorganic polymer film. Illustrative examples of inorganic materialssuitable as the insulating layer include silicon oxide, silicon nitride,aluminum oxide, barium titanate, barium zirconium titanate and the like;illustrative examples of organic polymers for the insulating layerinclude polyesters, polycarbonates, poly(vinyl phenol), polyimides,polystyrene, poly(methacrylate)s, poly(acrylate)s, epoxy resin and thelike. The thickness of the insulating layer is, for example from about10 nanometers to about 500 nanometers depending on the dielectricconstant of the dielectric material used. An exemplary thickness of theinsulating layer is from about 100 nanometers to about 500 nanometers.The insulating layer may have a conductivity that is for example lessthan about 10⁻¹² S/cm.

The insulating layer, the gate electrode, the semiconductor layer, thesource electrode, and the drain electrode are formed in any sequence aslong as the gate electrode and the semiconductor layer both contact theinsulating layer, and the source electrode and the drain electrode bothcontact the semiconductor layer. The phrase “in any sequence” includessequential and simultaneous formation. For example, the source electrodeand the drain electrode can be formed simultaneously or sequentially.The composition, fabrication, and operation of field effect transistorsare described in Bao et al., U.S. Pat. No. 6,107,117, the disclosure ofwhich is totally incorporated herein by reference.

The TFT devices contain a semiconductor channel with a width W andlength L. The semiconductor channel width may be, for example, fromabout less than 1 micrometers to about 5 millimeters, with a specificchannel width being about 5 micrometers to about 1 millimeter. Thesemiconductor channel length may be, for example, from about less than 1micrometer to about 1 millimeter with a more specific channel lengthbeing from about 5 micrometers to about 100 micrometers.

The source electrode is grounded and a bias voltage of generally, forexample, about 0 volt to about −80 volts is applied to the drainelectrode to collect the charge carriers transported across thesemiconductor channel when a voltage of generally about +40 volts toabout −80 volts is applied to the gate electrode.

Regarding electrical performance characteristics, a semiconductor layercomprising the solution processed semiconducting polymer has a carriermobility greater than for example about 10⁻³ cm²/Vs(centimeters²/Volt-second) and a conductivity less than for exampleabout 10−⁵ S/cm (Siemens/centimeter). The thin film transistors producedby the present process have an on/off ratio greater than for exampleabout 10⁴ at 20 degrees C. The phrase on/off ratio refers to thedifference between the source-drain current when the transistor is on tothe source-drain current when the transistor is off.

In embodiments, the charge transport capability (that is, for draincurrent and/or carrier mobility) of an electronic device made accordingto the present invention may have identical or better charge transportcapability than a comparative electronic device that is prepared throughconventional technologies.

The invention will now be described in detail with respect to specificpreferred embodiments thereof, it being understood that these examplesare intended to be illustrative only and the invention is not intendedto be limited to the materials, conditions, or process parametersrecited herein. All percentages and parts are by weight unless otherwiseindicated.

In the following examples, a polythiophene having the structural formula(11) was used for illustration.

Synthesis of polythiophene (11):

i) 5,5′-bis(3-dodecyl-2-thienyl)-2,2′-dithiophene: A solution of2-bromo-3-dodecylthiophene (11.5 grams, 34.92 mmol) in 40 milliliters ofanhydrous tetrahydrofuran (THF) was added slowly over a period of 20minutes to a mechanically stirred suspension of magnesium turnings (1.26grams, 51.83 mmol) in 10 milliliters of THF (tetrahydrofuran) in a 100milliliter round-bottomed flask under an inert argon atmosphere. Theresultant mixture was stirred at room temperature of about 22° C. to 25°C. for 2 hours, and then at 50° C. for 20 minutes before cooling down toroom temperature. The resultant mixture was then added via a cannula toa mixture of 5,5′-dibromo-2,2′-dithiophene (4.5 grams, 13.88 mmol) and[1,3-bis(diphenylphosphino]dichloronickel (II) (0.189 gram, 0.35 mmol)in 80 milliliters of anhydrous THF in a 250 milliliter round-bottomedflask under an inert atmosphere, and refluxed for 48 hours.Subsequently, the reaction mixture was diluted with 200 milliliters ofethyl acetate, was washed twice with water and with a 5 percent aqueoushydrochloric acid (HCl) solution, and dried with anhydrous sodiumsulfate. A dark brown syrup, obtained after evaporation of the solvent,was purified by column chromotography on silica gel yielding5,5′-bis(3-dodecyl-2-thienyl)-2,2′-dithiophene as a yellow crystallineproduct in 55 percent yield, m.p. 58.9° C. The NMR spectrum of the aboveobtained compound was recorded at room temperature using a Bruker DPX300 NMR spectrometer:

¹H NMR (CDCl₃): δ 7.18 (d, J=5.4 Hz, 2H), 7.13 (d, J=3.6 Hz, 2H), 7.02(d, J=3.6 Hz, 2H), 6.94 (d, J=5.4 Hz, 2H), 2.78 (t, 4H), 1.65 (q, 1.65,4H), 1.28 (bs, 36H), 0.88 (m, 6H).

ii) Polymerization: A solution of5,5′-bis(3-dodecyl-2-thienyl)-2,2′-dithiophene (0.50 gram, 0.75 mmol) in10 milliliters of chloroform was added slowly over a period of about 5minutes to a well stirred mixture of FeCl₃ (0.40 gram, 2.47 mmol) in 5milliliters of chlorobenzene in a 100 milliliter round-bottomed flask ina dry atmosphere. The resultant mixture was heated at 60° C. for 24hours under a blanket of dry air. After the polymerization, the mixturewas diluted with 20 milliliters of methylene chloride and washed threetimes with water. The separated organic phase was stirred with 150milliliters of 7.5 percent of an aqueous ammonia solution for 45minutes, washed with water until the water phase is clear, and thenpoured into methanol to precipitate the crude polythiophene. The finalpolythiophene product, which was purified by soxhlet extraction withheptane, and then with chlorobenzene, showed the following molecularweight properties: M_(w) 22,950; M_(n) 17250 relative to polystyrenestandards.

COMPARATIVE EXAMPLE

A top-contact thin film transistor structure, as schematically describedby FIG. 3, was chosen as the primary test device configuration in thisComparative Example. The test device was comprised of an n-doped siliconwafer with a thermally grown silicon oxide layer of a thickness of about110 nanometers thereon. The wafer functioned as the gate electrode whilethe silicon oxide layer acted as the insulating layer and had acapacitance of about 32 nF/cm² (nanofarads/square centimeter). Thefabrication of the device was accomplished under ambient conditionswithout any precautions being taken to exclude the materials and devicefrom exposure to ambient oxygen, moisture, or light. The silicon waferwas first cleaned with methanol, air dried, and then immersed in a 0.01M solution of octyltrichlorosilane in toluene for about 10 minutes atroom temperature. Subsequently, the wafer was washed withdichloromethane, methanol and air-dried. The semiconductor polythiophenelayer of about 30 nanometers to about 100 nanometers in thickness wasthen deposited on top of the silicon oxide insulating layer by spincoating a hot solution of the polythiophene (11) (at the temperaturemore than 60° C.) in dichlorobenzene at a speed of 1,000 rpm for about35 seconds, and dried in vacuo at 80° C. for 20 hours.

The evaluation of field-effect transistor performance was accomplishedin a black box at ambient conditions using a Keithley 4200 SCSsemiconductor characterization system. The carrier mobility, μ, wascalculated from the data in the saturated regime (gate voltage,V_(G)<source-drain voltage, V_(SD)) accordingly to equation (1)I _(SD) =C _(i)μ(W/2L) (V _(G) −V _(T))²  (1)where I_(SD) is the drain current at the saturated regime, W and L are,respectively, the semiconductor channel width and length, C_(i) is thecapacitance per unit area of the insulating layer, and V_(G) and V_(T)are, respectively, the gate voltage and threshold voltage. V_(T) of thedevice was determined from the relationship between the square root ofI_(SD) at the saturated regime and V_(G) of the device by extrapolatingthe measured data to I_(SD)=0.

An important property for the thin film transistor is its current on/offratio, which is the ratio of the saturation source-drain current whenthe gate voltage V_(G) is equal to or greater than the drain voltageV_(D) to the source-drain current when the gate voltage V_(G) is zero.

At least five thin film transistors were prepared with dimensions of W(width)=5,000 μm and L (length)=60 μm. The following properties wereobtained and summarized in Table 1.

The performance of the devices could be improved by thermal annealing.This was accomplished by first heating the devices in an oven to atemperature of about 150° C. for about 15 minutes, and then cooling themdown to room temperature before evaluation again.

EXAMPLE

a) Dispersion of Polythiophene (11)

Polythiophene (11) was dissolved in dichlorobenzene at 0.3 wt % level byheating to about 120° C. The solution was filtered through a 0.2 μmsyringe filter while it was hot. Yellow to reddish clear solution wasobtained. The hot solution was allowed to cool down to room temperaturewhile an ultrasonic vibration was applied with a 100 W sonicator at 42kHz for 10 to 15 minutes. The yellow-reddish solution became dark-purplewhen it was completely cooled to room temperature. A stable dispersionwas obtained, which can be stored at room temperature for weeks withoutvisually observable precipitation or gelling.

b) TFT Device Fabrication and Characterization

Thin film transistors were fabricated and evaluated using the proceduresof Comparative Example. In lieu of a hot solution of the polythiophene(11) in dichlorobenzene of the Comparative Example, a dispersion of thepolythiophene (11) in dichlorobenzene as prepared above was used to makethe semiconductor layer by spin coating at room temperature for 80seconds. Using the transistors with the same dimension (W=5000 mm, L=60mm), the following average properties from at least five separatetransistors are summarized in table 1. Thermal annealing was performedas described before to enhance device performance. TABLE 1 Beforeannealing After annealing Mobility Mobility Experiments (cm²/V · s)On/off ratio (cm²/V · s) On/off ratio Comparative 0.013-0.038 >10⁶0.05-0.12 ˜10⁷ Example Example 0.029-0.045 >10⁶ 0.076-0.12  ˜10⁷

The above results show that while the solution of polythiophene (11) indichlorobenzene at room temperature could not be properly coated viasolution processes such as spin coating, the solution could be coated atan elevated temperature of more than 60 degree C. to give asemiconductor layer that provided useful TFT properties (ComparativeExample). On the other hand, in the Example, the dispersion ofpolythiophene (11) in dichlorobenzene could be satisfactorily processedat room temperature by spin coating to give a semiconductor layer thatprovided TFT properties (Example) identical to those obtained in theComparative Example.

1. A composition including a polymer and a liquid, wherein the polymerexhibits lower solubility in the liquid at room temperature but exhibitsgreater solubility in the liquid at an elevated temperature, wherein thecomposition gels when the elevated temperature is lowered to a firstlower temperature without agitation, wherein the viscosity of thecomposition results from a process comprising (a) dissolving at theelevated temperature at least a portion of the polymer in the liquid;(b) lowering the temperature of the composition from the elevatedtemperature to the first lower temperature; and (c) agitating thecomposition to disrupt any gelling, wherein the agitating commences atany time prior to, simultaneous with, or subsequent to the lowering theelevated temperature of the composition to the first lower temperature,wherein the amount of the polymer dissolved in the liquid at theelevated temperature ranges from about 0.2% to about 5% based on thetotal weight of the polymer and the liquid.
 2. The composition of claim1, wherein the polymer is a self-organizable polymer.
 3. The compositionof claim 1, wherein the polymer is a semiconductor.
 4. The compositionof claim 1, wherein the polymer is polythiophene.
 5. The composition ofclaim 1, wherein the composition further comprises a different liquid,wherein the polymer is less or not capable of dissolving in thedifferent liquid compared to the liquid.
 6. The composition of claim 1,wherein there is visibly observable gelled material.
 7. The compositionof claim 1, wherein there is no visibly observable gelled material. 8.The composition of claim 1, wherein the liquid is selected from thegroup consisting of dichloroethane, chloroform, tetrahydrofuran,chlorobenzene, dichlorobenzene, trichlorobenzene, nitrobenzene, toluene,xylene, mesitylene, 1,2,3,4-tetrahydronaphthelene, dichloromethane,trichloroethane, 1,1,2,2-chloroethane, and a mixture thereof.
 9. Thecomposition of claim 5, wherein the different liquid is selected fromthe group consisting of methanol, ethanol, isopropanol, hexane, heptane,acetone, water, and a mixture thereof.
 10. The composition of claim 1,wherein the viscosity is compatible with spin coating and inkjetprinting.
 11. A composition having an inkjet-printing-compatibleviscosity at room temperature and including a semiconductor polymer anda liquid, wherein the polymer exhibits lower solubility in the liquid atroom temperature but exhibits greater solubility in the liquid at anelevated temperature, wherein the composition gels when the elevatedtemperature is lowered to a first lower temperature without agitation,wherein the amount of the polymer dissolved in the liquid at theelevated temperature ranges from about 0.2% to about 5% based on thetotal weight of the polymer and the liquid.
 12. The composition of claim11, wherein the polymer is a self-organizable polymer.
 13. Thecomposition of claim 11, wherein the polymer is polythiophene.
 14. Thecomposition of claim 11, wherein the composition further comprises adifferent liquid, wherein the polymer is less or not capable ofdissolving in the different liquid compared to the liquid.
 15. Thecomposition of claim 11, wherein there is visibly observable gelledmaterial.
 16. The composition of claim 11, wherein there is no visiblyobservable gelled material.
 17. The composition of claim 11, wherein theliquid is selected from the group consisting of dichloroethane,chloroform, tetrahydrofuran, chlorobenzene, dichlorobenzene,trichlorobenzene, nitrobenzene, toluene, xylene, mesitylene,1,2,3,4-tetrahydronaphthelene, dichloromethane, trichloroethane,1,1,2,2-chloroethane, and a mixture thereof.
 18. The composition ofclaim 14, wherein the different liquid is selected from the groupconsisting of methanol, ethanol, isopropanol, hexane, heptane, acetone,water, and a mixture thereof.